The present invention relates generally to methods for eliminating or reducing potential damage to devices from electrostatic discharge or electrical overstress and, more particularly, to methods for reducing such damage to electronic components such as, but not limited to, a magnetoresistive head forming part of a disc drive.
Damage due to electrostatic discharge (ESD) and/or electrical overstress (EOS) costs industry in damaged and irreparable goods. More specifically, ESD/EOS damage is a particular problem in the electronics industry where the components are designed to conduct electricity in the first instance and where their continuously shrinking size renders them increasingly susceptible to such damaging effects. Generally, ESD refers to actual discharges while EOS refers to the effects of such discharges or currents induced by such discharges or other electrical or magnetic fields. For present purposes, reference to one should be interpreted to include the other.
ESD, familiarly manifested by the lightning bolts or by the shock received when touching a door knob after walking across a carpet, can range from a few volts to as much as several thousand volts, resulting in extremely large transient currents. As electronic components shrink in size they become ever more susceptible to damage from smaller and small voltages and current.
ESD can arise in several different ways, most commonly as a result of triboelectric charging or induction. Triboelectric charging causes a charge build up due to the frictional engagement of two objects. That is, static charge builds up as a result of a series of contacts and separations of two objects. Consequently, a net charge of opposite sign builds up and remains on both of the objects after their separation. Where the object has good conductivity and is grounded, charge will flow to the ground. If the electric field generated by the separated charges is strong enough, an electrostatic discharge can occur in the form of a spark traveling across an air gap from one object towards an object at a lower electrostatic potential. This discharge can occur either as one object is brought next to one of the charged objects or as one object is separated from the other.
Static charges can also build up by induction. If a charged object is brought near an uncharged object, the electric field of the charged object will induce a charge in the uncharged object, generating an electric field and potentially a static discharge.
A goal in many industries is to determine methods and apparatus for reducing or eliminating static discharges. Companies that manufacture and assemble disc drives are one of the electronics industries affected by ESD/EOS damage. As noted above, present disc drives include a disc rotated at high speeds and a read/write head that xe2x80x9cfliesxe2x80x9d a microscopic distance above the disc surface. The disc includes a magnetic coating that is selectively magnetizable. As the head flies over the disc, it xe2x80x9cwritesxe2x80x9d information, data, to the disc drive by selectively magnetizing small areas of the disc; in turn, the head xe2x80x9creadsxe2x80x9d the data written to the disc by sensing the previously written selective magnetizations. The read/write head is affixed to the drive by a suspension assembly and electrically connected to the drive electronics by an electrical interconnect. This structure (suspension, electrical interconnect, and read/write head) is commonly referred to in the industry as a Head Gimbal Assembly, or HGA.
More specifically, currently manufactured and sold read/write heads include an inductive write head and a magnetoresistive (MR) read head or element or a xe2x80x9cgiantxe2x80x9d magnetoresistive (GMR) element to read data that is stored on the magnetic media of the disc. The write head writes data to the disc by converting an electric signal into a magnetic field and then applying the magnetic field to the disc to magnetize it. The MR read head reads the data on the disc as it flies above it by sensing the changes in the magnetization of the disc as changes in the voltage or current of a current passing through the MR head. This fluctuating voltage in turn is converted into data. The read/write head, along with a slider, is disposed at the distal end of an electrical interconnect/suspension assembly.
Other types of read heads, such as inductive read heads, are known, but the MR and GMR elements enable the reading of data that is stored more densely than that which was allowed with the use of inductive read element technology. MR and GMR read elements are much more sensitive to current transients resulting from voltage potentials and thermal gradients, however, then the previous read element technologies. It is now becoming increasingly necessary to manage environmental electrostatic charge levels to as low as 3.3 volts during HGA manufacturing processes so as not to damage the MR and GMR elements. Failing to do so, or failing to provide an avenue for the safe discharge of the accumulated electrostatic charge can result in damage to the MR and GMR heads.
Damage to an MR or GMR head can be manifested as physical damage and/or magnetic damage. In the former, melting of the read element in the head can occur because of the heat generated by the transient current of the discharge. Magnetic damage can occur in the form of loss of sensing ability and instability. Furthermore, direct discharge into the head is not necessary to create the damage. Damaging current flow in the head can also reportedly be created through electromagnetic interference as a result of a distant discharge.
An exploded view of a typical electrical interconnect/suspension assembly 10 is shown in FIG. 1, which illustrates several components including a suspension 12 and an interconnect 14. It will be understood that the actual physical structures of these components may vary in configuration and that the assembly shown in FIG. 1 is meant to be illustrative of the prior art only. Typically, the suspension 12 will include a base plate 16, a radius (spring region) 18, a load beam 20, and a gimbal 22. At least one tooling aperture 24 may be included. An interconnect 14 may include a base 26, which may be a synthetic material such as a polyimide, that supports typically a plurality of electrical traces or leads 28 of the interconnect. The electrical interconnect 14 may also include a polymeric layer that encapsulates selected areas of the electrical traces or leads 28.
Stated otherwise, suspension 12 is essentially a stainless steel support structure that is secured to an armature in the disc drive. A read/write head (not shown) is attached to the tip of the suspension 12 with adhesive or solder, generally. The aforementioned electrical interconnect 14 is terminated to bond pads on the read/write head and forms an electrical path between the drive electronics (not shown) and the read and write elements in the read/write head. The electrical interconnect 14 is typically comprised of individual electrical conductors supported by an insulating layer of polyimide and typically covered by a cover layer. Prior to the time that the HGA is installed into a disc drive, the electrical interconnect is electrically connected to the read and write elements, but is not connected to the drive electronics. As a result, the individual conductors 28 that make up the electrical interconnect 14 can easily be charged by stray voltages, thereby creating a voltage potential across the sensitive MR or GMR read elements, which when discharged results in damaging current transients through the read element.
The components shown in FIG. 1 as well as all those associated with disc drives are small and continually decreasing in size. Consequently, any tolerance for ESD/EOS damage of the components during the assembly process is also continuously decreasing while their susceptibility to damage during assembly is increasing. As noted, an ESD can actually damage or destroy circuit pathways in small electronic parts, such as an MR head, requiring the head to be discarded.
It is desirable to have a method of creating and removing electrical shorts in sensitive electronic components. More specifically, it is desirable to have a method of creating and removing an electrical short to prevent ESD/EOS damage in an MR head.
According to a first aspect of the invention, there is provided an intermediate article of manufacture of a magnetoresistive head with a protective device. The device includes a sensor element having terminal pads and a shunt element having a first and second terminal connected across the sensor element for shunting the sensor element to discharge static electrical charge during the manufacture of the magnetoresistive head. The shunt element being a piece of solder extending between the first and second terminals.
According to a second aspect of the invention, there is provided a method for substantially protecting an electronic component from EDS/EOS, the component including a pair of spaced apart leads for conducting current. The method includes the step of applying a conductive element between the pair of spaced part leads wherein the conductive element provides a shunt between the pair of spaced apart leads.
According to a third aspect of the invention, there is provided an intermediate article of manufacture of a magnetoresistive head with a protective device. The article includes a sensor element having terminal pads and means connected across the sensor element for shunting the sensor element to discharge static electrical charge during the manufacture of the magnetoresistive head.